This invention relates generally to devices for filtering and separating liquids. More particularly, the present invention relates to filters for the fuel supply system or lubricating oil of an internal combustion engine and removing foreign particles and separating water therefrom.
The absence of high standards of quality control in diesel fuel supplies dictates that an effective fuel filter be incorporated into the fuel supply system of a diesel engine. It is not uncommon for diesel fuel to have significant quantities of abrasive particles and water. The abrasive particles present the potential for permanent damage to components of the fuel injection pump. The abrasive particles can also adversely affect the performance of the pump by destroying the ability of the fuel injection pump to precisely meter and deliver fuel at high pressures. The presence of water in the diesel fuel supply can cause corrosion of engine components, and during freezing conditions, can result in interruption of the fuel injection system and/or seizure of moving components. Similarly, water and particulate matter in the lubricating oil must be removed to minimize wear of engine parts.
Commonly, filters employ a disposable filter cartridge which is replaced at pre-established intervals of filter usage. The cartridge is secured to a base assembly that is fixedly mounted to the engine header or some other fixed location.
Current filter assemblies require a plurality of seals to seal the cartridge to the base assembly. The cartridge and base assembly are sealed to ensure that the fluid being filtered does not bypass the filter element in the cartridge. Additional seals may be employed to prevent short circuiting internal flow paths within the cartridge. The use of multiple seals increases the number of components, thereby increasing the cost of manufacture. In addition, the use of multiple seals increases the probability that a leak will occur.
For most, if not all diesel fuel delivery systems, as fuel circulates through the fuel filter, air pockets are formed in the fuel filter. The air pockets normally form at the top of the fuel filter. Air bubbles tend to form in the fuel as a result of gassing when exposed to changes in pressure. For pressurized fuel delivery systems, the air pockets tend to disintegrate over time and/or the stream of bubbles present in the fuel is of a relatively small magnitude. The air pockets generally do not result in the formation of large air bubbles in the fuel supply partly due to the vapor pressure of the pressurized fuel. Consequently, for pressurized systems, air pockets in the fuel filter do not present a significant problem or obstacle to the circulation of fuel through the fuel filter and the delivery of fuel to the engine.
However, in vacuum applications, the formation of air pockets in the fuel circulating through the filter can present a more significant problem. The air pockets are much more resistant to absorption over time in vacuum systems. Moreover, the vacuum suction exerted may result in the formation of tiny air bubbles or "gassing" in the fuel. This is especially true as the filter element approaches the end of its useful life and the pressure drop across the filter media increases. This increasing restriction to flow causes more air to be pulled from the fuel as the differential pressure between the clean side and the dirty side increases. In of themselves, these individual tiny bubbles do not present a problem to normal vehicle operation as they are easily ingested by the fuel injection pump. When subjected to pump charging pressures, the tiny bubbles are ordinarily reabsorbed by the fuel.
The problems in vacuum suction systems initially arise on the clean side of the filter element where the small bubbles inevitably collect, agglomerate and form air pockets, e.g., large bubbles. The large bubble formation will continue over a period of time until the physical attitude of the filter element changes due to vehicle maneuvering, etc. When these relative large air pockets or bubbles escape into the fuel flow, they are not easily ingested and may cause engine operating problems such as stalling or engine misfire.